Tape end warning apparatus

ABSTRACT

A tape end warning apparatus comprises an alarm switch which is closed in response to the detection of a terminal end of a running tape being reached during a record or playback operation of a tape recorder, and an oscillator circuit which is activated by the closure of the switch. The oscillator circuit produces an alarm signal which is fed to an amplifier inherently contained in a tape recorder so as to give off an audible alarm through a loudspeaker which is connected with the amplifier.

RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 713,344, filedAug. 11, 1976 now U.S. Pat. No. 4,157,575.

BACKGROUND OF THE INVENTION

The invention relates to a tape end warning apparatus for indicating theend of a running tape in a tape recorder.

A variety of devices are heretofore available which indicate to theoperator of a tape recorder that a terminal end of a running magnetictape is reached during a record or playback operation. By way ofillustration, an electrically conductive foil may be applied to theterminal end of the tape so as to be detected for activating an alarmbuzzer; or the mechanical tension in the tape may be utilized to detectthat the terminal end of the tape is reached, thereby operating amechanical stop assembly to interrupt the operation of a tape drivemotor in an automatic manner. However, these prior arrangements add tothe complexity of the tape recorder into which they are incorporated,and additionally requires a relatively large space for their provision.Thus, their provision stands in the way to the miniaturization of thetape recorder. Since a miniature size tape recorder which employs amicro-cassette has a limited internal space which cannot afford to theprovision of a mechanical stop mechanism and since the tape cassette isof a size which prohibits further apparatus from being applied to amagnetic tape disposed therein, the known arrangements are completelyunusable with such a miniature size tape recorder. Nevertheless, it isdesirable that some means be provided to indicate to the operator that aterminal end of a running tape contained in a micro-cassette is reached.The desirability will be appreciated if one considers a recording ofsome information with the tape recorder, where it will be noted that theoperator may continue to run the recorder without noticing the fact thatthe tape end is reached and there is no longer any available length oftape on which to record the information, thus resulting in a seriousfailure to record the information. However, there has been no availablearrangement end being reached in a tape recorder which cannot afford tothe provision of any additional mechanism in the interior thereof.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a tape end warning apparatusfor use in a tape recorder which eliminates the above disadvantages bygiving an audible alarm indicative of the end of the tape runningthrough an amplifier and a loudspeaker which are inherently provided inthe tape recorder.

In a first embodiment of the invention (see FIGS. 1 to 11 and 16), thereis provided a tape end warning apparatus utilizing an audio amplifierand a loudspeaker inherently provided in the tape recorder which areconnected with an audible alarm generator through an alarm switch whichis closed when the tape end is detected. Because the amplifier and theloudspeaker are inherently provided in the tape recorder, there is noadditional space requirement, thus enabling it to be incorporated into aminiature size tape recorder.

In a second embodiment of the invention (see FIGS. 12 to 15), there isprovided a tape end warning apparatus which utilizes an amplifier and aloudspeaker inherently provided in a tape recorder and whichadditionally includes an alarm switch, adapted to be operated inresponse to the detection of a tape end, and a switching transistor, thearrangement being such that when a running tape reaches its terminalend, the switch is closed to render the transistor conductive, whereuponthe amplifier has its output terminal forcibly connected with theloudspeaker even during a record operation. Simultaneously, a positivefeedback is applied to the amplifier to cause it to oscillate, and theoscillation is applied to the loudspeaker, which therefore gives off anaudible alarm indicative of the tape end. It should be noted that aseparate oscillator need not be provided to produce the audible alarm.

Further details, features and advantages of the invention will becomeapparent from the following description of embodiments thereofillustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a tape end warning apparatus constructedin accordance with one embodiment of the invention;

FIG. 2 is a plan view of a mechanism which operates an alarm switch;

FIG. 3 is a circuit diagram which illustrates the manner of amalfunctioning which may occur in the apparatus shown in FIG. 1;

FIG. 4 is a circuit diagram of means for preventing the malfunctioningillustrated in FIG. 3;

FIG. 5 is a circuit diagram of means for preventing an audible alarmfrom being given off by a loudspeaker when an earphone is being used;

FIG. 6 is a circuit diagram of means for preventing an audible alarmfrom being generated as by closure of the alarm switch in response tothe vibrations;

FIG. 7 is a circuit diagram of means which prevents a howling;

FIG. 8 is a circuit diagram of another means which prevents a howlingeffect;

FIG. 9 is a circuit diagram of a tape end warning apparatus whichincorporates a tape end detector comprising a capacitor;

FIG. 10 is a perspective view of a micro-cassette, illustrating amechanism for providing a sliding contact between a resilient slidingcontact and a movable contact;

FIG. 11 is a circuit diagram of a modification of the tape end detectorshown in FIG. 9 which includes a switch adapted to be operated in gangedrelationship with a pause button;

FIG. 12 is a circuit diagram of a tape end warning apparatus constructedaccording to another embodiment of the invention;

FIG. 13 is a circuit diagram of means which prevents an audible alarmfrom being given off during a playback operation;

FIG. 14 is a circuit diagram of alternate means for preventing anaudible alarm from being given off during a playback operation;

FIG. 15 is a circuit diagram of a tape end warning apparatus accordingto a further embodiment of the invention which incorporates a tape enddetector comprising a capactor; and

FIG. 16 is a circuit diagram of a combination of circuits shown in FIGS.6 and 7 which is adapted to be incorporated into a tape recorder.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Initially, an apparatus of the invention will be described which has anoscillator circuit formed separately from an audio amplifier inherentlyprovided in a tape recorder. Referring to FIG. 1, the tape recordershown includes an amplifier 1, shown in a block indicated by phantomlines 1A. The amplifier 1 functions to amplify a reproduced outputsignal from a playback head, not shown, and feed it to a loudspeaker 2when the tape recorder is in its playback mode, and to amplify an outputsignal from a microphone, not shown, and feed it to a record head, notshown, when the tape recorder is in its record mode.

The circuit arrangement of the amplifier 1 is conventional. However,briefly describing the amplifier circuit, an output signal from aplayback head or a microphone is applied through a coupling capacitor 3to a variable resistor 4 which represents a volume control. From thevariable resistor 4, the output signal is passed through a seriescombination of a resistor 5 and a capacitor 6 to be applied to the baseof a first amplifying transistor 7, which base is applied with anoperative voltage by a voltage divider formed by a pair of resistors 10,11 connected in series across a positive and a negative bus 8, 9 of apower source. The collector of the transistor is connected through aresistor 12 with the bus 8 while the emitter is connected through aresistor 13 to the bus 9. The amplified output from the transistor 7 isapplied through a coupling capacitor 14 to the base of a secondamplifying transistor 15, which base is supplied with an operatingvoltage by a voltage divider comprising a pair of series resistors 16,17 which are connected in a manner similar to the resistors 10, 11. Theemitter of the transistor 15 is connected with the negative bus 9through a series circuit comprising a pair of resistors 18, 19, theresistor 18 being shunted by a capacitor 20. The junction between theresistors 18, 19 is connected through a series circuit comprising aresistor 23 and a capacitor 22 with a secondary coil 21a of an outputtransformer 21, thereby providing a negative feedback. The collector ofthe transistor 15 is connected with the positive bus 8 through a primarycoil 24a of a coupling transformer 24.

The final stage of the amplifier 1 comprises a push-pull amplifiercircuit which is coupled with the transistor 15 through the coupling 24.The push-pull circuit comprises a pair of transistors 25, 26 havingtheir base electrodes connected with the opposite ends of a centertapped secondary winding 24b of the transformer and having their emitterelectrodes connected in common and with the positive bus 8 through aresistor 29, with a pair of capacitors 27, 28 connected across thecollector and base of the respective transistors. The center tap of thesecondary winding 24b is connected with the junction between a pair ofresistors 30, 31 connected across the positive and negative buses andforming a voltage divider. The collector electrodes of the transistors25, 26 are connected with the opposite ends of a center tapped primarycoil 21b of output transformer 21, with the center tap being connectedwith the negative bus 9. A protective resistor 32 is connected acrossthe secondary coil 21a of the output transformer 21.

The opposite ends of the secondary coil 21a are connected with anearphone jack 33, which comprises a movable contact 33a, and a pair ofstationary contacts 33b and 33c which are connected with the ends of thecoil 21a. Normally, the movable contact 33a is thrown to the stationarycontact 33b. The stationary contact 33c is connected with the negativebus 9, which may be connected with the ground. The movable contact 33ais also connected with a movable contact 34a of a record/playbackchangeover switch 34 which also includes a pair of stationary contacts34b and 34c. In the record mode of the tape recorder, the movablecontact is thrown to the stationary contact 34b, as shown, while in theplayback mode, the movable contact is thrown to the other stationarycontact 34c. The stationary contact 34b is connected with the negativebus 9 through a resistor 35 while the stationary contact 34c isconnected with a moving coil of the loudspeaker 2.

A tape end warning apparatus according to the invention is generallyshown at 1B and comprises an audio frequency oscillator 36, a couplingcapacitor 37 which feeds the output signal of the oscillator 36 to theinput end of the amplifier 1, an alarm switch 38 adapted to be closedwhen a terminal end of a running tape Tp (see FIG. 2) is reached, and aswitching transistor 39 responsive to the closure of the switch 38 forconnecting the output from the amplifier 1 to the loudspeaker 2. Theswitch 38 and the transistor 29 together from the alarm switch means.

In the embodiment shown, the oscillator 36 comprises a flipflop circuitformed by a multivibrator oscillator of a known form. The flipflopcomprises a pair of transistors 40, 41 having their collectors connectedwith a positive bus 8a through resistors 42, 45, respectively, andhaving their base connected with the positive bus 8 through resistors44, 43, respectively, and also connected with the collector of the othertransistor through capacitors 46, 47, respectively. The couplingcapacitor 37 has its one end connected with the collector of thetransistor 41 and its other end connected with the base of the inputtransistor 7 of the amplifier 1, thus serving to apply an output signalfrom the oscillator 36 to the amplifier 1.

The alarm switch 38 is connected with a positive power source, notshown, which feeds the oscillator 36, and is normally open. As indicatedin FIG. 2, the switch 38 may be disposed in the path of rocking motionof a movable member 49 which supports a supply shaft 48 for a runningtape Tp. When the running tape Tp reaches its terminal end, a resultingincrease in the tension of the tape acts through the shaft 48 to rockthe movable member 49 in a direction to close the switch 38. As is wellknown, a magnetic tape has its opposite ends anchored to a pair of tapehubs 50, 51, and is fed by the cooperation between a pinch roller 52 anda capstan 53. When the running tape Tp is entirely taken up on a tapetake-up shaft 54 and thus reaches its terminal end, the winding forceproduces an increase in the tape tension, whereupon the movable member49, pivotally mounted on a pin 49a, rocks in the direction of an arrowa₁ against the resilience of a spring 55 which normally maintains thetape supply shaft 48 in its home position, thus closing the switch 38.

As shown in FIG. 1, the switching transistor 39 has its base connectedwith the junction between the switch 38 and the resistors 42 to 45, andhas its collector connected with the stationary contact 33b of theearphone jack 33. The emitter of the transistor 39 is connected with thestationary contact 34c of the changeover switch 34. When the switch 38is closed, an operating voltage is applied to the base of transistor 39to render it conductive.

In operation, in either a record or playback condition of the taperecorder, as a terminal end of the running tape Tp is reached, theresulting increase in the tape tension causes the movable member 49 torock, thus closing the alarm switch 38. Thereupon, the oscillator 36 andthe transistor 39 are fed from the positive bus 8a, whereby theoscillator 36 begins to oscillate, with its output signal of an audiofrequency being coupled through the capacitor 37 to the base of thetransistor 7 which is contained in the amplifier 1. As a result, theoutput signal is amplified by the amplifier 1 and appears across thesecondary coil 21a of the output transformer 21. Since the transistor 39is rendered conductive, the loudspeaker 2 is connected across thesecondary coil 21a, so that the output signal of an audio frequencyappearing across the secondary coil 21a is converted by the loudspeaker2 into an audible alarm, indicating that a terminal end of the runningtape Tp is reached.

Referring to FIG. 3, when an input signal e₀ applied to the inputterminal of the amplifier 1 has a sufficient amplitude to render thetransistor 39 conductive, it passes through paths a2, b2, c2, d2, e2 andf2, and thus is applied to the base of the transistor 39 through thecoupling capacitor 37, resistor 45 of the oscillator 36 and part of thebus 8a. This results in a conduction of the transistor 39, supplying thesignal which is to be applied to a record head, to the loudspeaker 2,preventing an intended recording operation.

In order to avoid the occurrence of such inconveniences FIG. 4 shows theconnection of a diode 56 in the portion of the bus 8a located betweenthe oscillator 36 and the switch 38, the diode being poled to prevent aflow of signal through the bus portion located between the switch 38 anda point T1a of the oscillator 36. It will be appreciated that thisprevents the input signal e₀ from being applied the base of theswitching transistor 39.

As will be made apparent from the foregoing description, the tape endwarning apparatus of the present embodiment allows the loudspeaker 2 togive off the audible alarm indicative of the terminal end of the runningtape even during a record mode of the tape recorder, since theloudspeaker 2 is connected with the output terminal of the amplifier 1through the switched transistor 39. However, under certain circumstanceswhere the fact of maintaining the tape recorder in a record mode shouldbe kept in secret, the production of the audible alarm by theloudspeaker 2 is undesirable. Generally, such a secret recording isperformed by monitoring the record by an earphone, not shown, which isinserted into the jack 33 of the tape recorder. Hence, it will beconvenient to produce the audible alarm through the earphone. Though thedesired result can be achieved by the addition of a switch or the like,this requires an increase in the number of parts and an additional spacerequirement. This can be avoided by a modification of the electricalinterconnection between the jack 33 and the transistor 39, withoutrequiring additional parts and increasing the space requirementtherefor.

The collector of the switching transistor 39 is connected with thestationary contact 33b of the jack 33 in the circuit arrangement shownin FIG. 1. However, it may be connected with the movable contact 33a ofthe jack 33, as shown in FIG. 5. With this modification in theconnection of the collector of the transistor 39, so long as an earphoneis inserted into the jack 33, the loudspeaker 2 remains disconnectedfrom the secondary coil 21a of the output transformer 21 even if thetransistor 39 is rendered conductive, and therefore cannot give off theaudible alarm. Instead the earphone (not shown) which is inserted intothe jack 33 will be connected across the coil 21a to provide areproduction of the audible alarm. The reproduction of the audible alarmfrom the loudspeaker 2 may also be prevented by the insertion of a plug(not shown) which is similar to the earphone jack but which is notconnected with any earphone. It should be understood that during anormal recording other than a secret recording, and thus when noearphone is inserted into the jack 33, the loudspeaker 2 can give offthe audible alarm.

It should be understood that the audio frequency oscillator 36 is notlimited to the flipflop circuit shown, but may be of any design capableof producing an output signal of an audio frequency. Similarly, thealarm switch 38 may be closed by other means than that shown, the onlyrequirement being that the switch be closed by detecting the fact thatthe running tape has reached its terminal end.

Referring to FIG. 6, there is shown another embodiment which preventsthe generation of the audible alarm in response to a momentary closureof the alarm switch which may be caused by an extraneous factor such asvibrations of the tape recorder during a portable use thereof, when therunning tape does not reach its terminal end. The circuit arrangement isgenerally similar to that shown in FIG. 1 except that a delay circuit 60is connected in the circuit path between the switch 38 and theoscillator 36. The delay circuit 60 comprises a pair of transistors 61,62, resistors 63, 64 and a capacitor 65. The emitter of the transistor61 is connected with one terminal of the switch 38 and its collector isconnected with the oscillator 36 of the warning apparatus 1B as well asthe switching transistor 39. The base of the transistor 61 is connectedwith the collector of the other transistor 62, the emitter of which isconnected with the ground, and the resistor 63 is connected across theemitter of the transistor 61 and the base of the transistor 62. Thecapacitor 65 is connected in series with the resistor 63, and thus formsa time constant circuit which determines the delay time of the circuit60. The capacitor 65 is shunted by the discharge resistor 64.

In operation, assuming that the alarm switch 38 is momentarily closed asby oscillations during the tape running, the bus 8a feeds current whichcharges the capacitor 65 through the resistor 63. During the time thecapacitor 65 is being charged, the transistors 61 and 62 cannot conduct,and therefore the warning apparatus 1B cannot operate. Hence, if theswitch 38 which is momentarily closed re-opens within such delay time,the warning apparatus remains inoperative, and hence an inadvertentclosure of the alarm switch 38 in response to oscillations tooscillations cannot produce a false warning indicative of tape end. Whenthe switch 38 re-opens, the capacitor 65 is discharged through theresistor 64.

When the running tape has reached its terminal end, the alarm switch 38is closed as before, so that the transistors 61, 62 conduct after a timedelay determined by the resistor 63 and the capacitor 65. Thus the bus8a is connected with the warning apparatus 1B through the alarm switch38 and the delay circuit 60, thus operating it to warn the operator ofthe fact that a terminal end of the running tape has been reached.

FIG. 7 shows a further embodiment in which a howling of a microphone isprevented by connecting the microphone to the ground through an activeelement which operates upon the generation of an audible alarm. Thecircuit arrangement shown in FIG. 7 is generally similar to that shownin FIG. 1 except that a record amplifier 67 is connected to feed asignal from a microphone 66 connected to its input, through a couplingresistor 68 to the coupling capacitor 3 (see FIG. 1) at the inputterminal of the amplifier 1. As shown, the amplifier 67 is fed from thebus 8. The signal amplified by the amplifier 1 is supplied to a recordhead, not shown. In addition, the circuit arrangement shown in FIG. 7includes an active element or a variable impedance element in the formof a transistor 69. The collector of the transistor 69 is connected withthe output terminal of the amplifier 67, and its emitter is connectedwith the ground or the negative bus 9. The base of the transistor 69 isconnected with the junction between the switch 38 and the oscillator 36.

During a record mode of the tape recorder, as the running tape reachesits terminal end, the closure of the switch causes the tape end warningapparatus to operate, thereby indicating the terminal end of the tapethrough the audible alarm. In addition, the closure of the switch 38permits a sufficient bias to be applied to the base of the transistor 69to render it conductive. Thereupon, the output terminal of the recordamplifier 67 is short-circuited to the ground and thus is prevented frombeing an input to the amplifier 1, which only receives the oscillationoutput from the oscillator 36. In this manner, a howling is effectivelyavoided while allowing the audible alarm to be given off by theloudspeaker 2.

Instead of short-circuiting the output terminal of the amplifier 67 tothe ground, the output terminal of the microphone 66 may be directlyshort-circuited to the ground by similar means. As a furtheralternative, the power connection of the amplifier 67 with the bus 8 maybe interrupted by corresponding means.

FIG. 8 shows a modification of the circuit arrangement shown in FIG. 7in that a transistor which is provided in the amplifier circuit for thepurpose of AGC (automatic gain control) is utilized to prevent a howlingwhen producing an audible alarm. In FIG. 8, during a record mode of thetape recorder, an output from the microphone 66 which is to be recordedis amplified by the record amplifier 67 and then applied through thecoupling resistor 68 to the coupling capacitor 3 (see FIG. 1) at theinput terminal of the amplifier 1. Subsequently, the amplified outputfrom the amplifier 1 is supplied to a record head, not shown. An AGCcircuit comprising a resistor 70, a diode 71, a variable impedanceelement in the form of a transistor 69a and a capacitor 72 is connectedacross the output terminal of the amplifier 1 and the output terminal ofthe record amplifier 67 to apply an AGC action, which maintains aconstant optimum level at the output of the amplifier 1. The transistor69a has its collector connected with the output terminal of theamplifier 67 through the capacitor 72, its emitter connected to theground and its base connected with the output terminal of the amplifier1 through the series combination of the diode 71 and resistor 70.

The AGC transistor 69a is effectively utilized for the purpose of theinvention. A diode 73 is connected between the switch 38 and theoscillator 36 and is poled to prevent a current flow from the oscillatorto the switch. A series circuit comprising a resistor 74 and a diode 75is connected between the base of the transistor 69a and the cathode ofthe diode 73, and a capacitor 76 is connected across the base andemitter of the transistor 69a.

With this embodiment, while a sufficient length of tape is availableduring a record operation of the tape recorder, the transistor 69aresponds to the output signal of the amplifier 1 by applying an AGCaction. However, when the running tape reaches its terminal end, theclosure of the switch 38 activates the tape end waring apparatus forgiving off an audible alarm. The closure of the switch 38 causes thecapacitor 76 to be charged through a path including the diode 73,resistor 74 and diode 75, whereby an operating voltage is applied to thebase of the transistor 69a to render and maintain it conductive. As itconducts, the amplification factor of the record amplifier 67 issubstantially attenuated, thus preventing a howling effect as a resultof an input signal to the microphone 66. The alarm output from theoscillator 36 is applied to the input of the amplifier 1 in a normalmanner, thereby causing the loudspeaker 2 to give off an audible alarm.

Referring to FIGS. 9 and 10, another form of tape end warning apparatuswill be described below in which a switching transistor is renderedconductive to operate an audio frequency oscillator to thereby supplyits oscillation output to the amplifier contained in the tape recorderso as to be given off by the loudspeaker thereof, by electricallydetecting the interruption of rotation of a tape supply shaft and a tapetake-up shaft which occurs when the running tape reaches its terminalend. In FIG. 9, an amplifier 101 of the tape recorder is shown in ablock 101A indicated by phantom lines. The amplifier 101 is operative,during a playback mode of the amplifier, to amplify an output signalreproduced by a playback head, not shown, and supply it to a loudspeaker102, and is operative, during a record mode of the tape recorder, toamplify an output signal from a microphone, not shown, and supply it toa record head, not shown.

The amplifier 101 is conventional as was the amplifier 1 mentionedabove. The output signal from either a playback head or microphone iscoupled through the coupling capacitor 103 to be applied across anadjustable resistor 104 which represents a volume control. An adjustedoutput signal from the adjustable resistor 104 is fed through a seriescombination of a resistor 105 and a capacitor 106 to the base of a firstamplifying transistor 107. An operating voltage is applied to the baseby a voltage divider formed by a series of resisters 110, 111, 112connected across a positive supply bus 108 and a negative supply bus109, the junction between the resistors 111 and 112 being connected withthe base. The transistor 107 has its collector connected with thejunction between the resistors 110, 111, and has its emitter connectedwith the bus 109 through a resistor 113. The amplified signal from thetransistor 107 is fed through a coupling capacitor 114 to the base of asecond amplifying transistor 115, the emitter of which is connected withthe bus 109 through a series circuit of resistors 118, 119. The resistor118 is shunted by a capacitor 120, and the junction between theresistors 118,119 is connected through a series combination of aresistor 123 and a capacitor 122 with the secondary coil 121a of anoutput transformer 121, thus providing a negative feedback. Thecollector of the transistor 115 is connected with the bus 108 throughthe primary coil 124a of a coupling transformer 124.

The final stage of the amplifier 101 is formed by a push-pull amplifiercircuit which is coupled with the transistor 115 through the couplingtransformer 124. The transformer 124 has a secondary coil 124b, theopposite ends of which are connected with the base of a pair oftransistors 125, 126 having their emitters connected in common and withthe bus 108 through a resistor 129. The secondary coil 124b has a centertap which is connected with the respective buses through a pair ofresistors 116, 117. The collectors of the transistors 125, 126 areconnected with the opposite ends of a center tapped, primary coil 121bof an output transformer 121, with the center tap being connected withthe negative bus 109. In addition, a capacitor 127 is connected betweenthe center tap and the emitter of the respective transistors 125, 126.The final stage induces an amplified output signal across the secondarycoil 121a, across which is connected a protective resistor 132. It is tobe noted that a voltage regulation resistor 130 is connected in the bus108.

An earphone jack 133 is connected across the secondary coil 121a. As isconventional, the jack 133 includes a movable contact 133a and a pair ofstationary contacts 133b, 133c which are connected across the secondarycoil. The movable contact 133a is normally maintained in contact withthe stationary contact 133b. The stationary contact 133c is alsoconnected with the negative bus 109. The movable contact 133a isconnected with a movable contact 134a of a record/playback changeoverswitch 134 having a pair of stationary contacts 134b, 134c. During arecord mode of the tape recorder, the movable contact 134a is thrown tothe stationary contact 134b, while during a playback mode, it is thrownto the other stationary contact 134c. A resistor 135 is connectedbetween the stationary contact 134b and the bus 109, and a loudspeaker102 is connected between the stationary contact 134c and the bus 109.

In accordance with the invention, a transistor 139 has its baseconnected through a resistor 136 with a tape end detector circuit 140.The collector of the transistor 139 is connected with the stationarycontact 133b of the earphone jack 133, while the emitter is connectedwith the other stationary contact 134c of the changeover switch 134. Thearrangement is such that an operating voltage is supplied to the base ofthe transistor 139 from the tape end detector circuit 140.

The tape end detector circuit 140 is shown in a block indicated byphantom lines 140A, and comprises a series circuit including at leasttwo capacitors C1, C2; a first and a second switching transistor 141,142 which are rendered conductive when the capacitors C1, C2 are chargedto given voltages; and three contact fingers 143, 144, 145 slidablyengaging the contact segments 146, 147, 148 for controlling the chargingof the copacitors C1, C2. More specifically, the base of the transistor139 is connected with the collector of the second switching transistor142, which has its emitter connected with the positive bus 108. The baseof the transistor 142 is connected with the collector of the firstswitching transistor 141, which has its emitter connected with theground. The capacitor C1 has one end connected through a resistor 149with the positive bus 108 and the other capacitor C2 has its end remotefrom the capacitor C1 connected with the ground. The junction T2abetween the capacitor C1 and the resistor 149 is connected with the baseof the transistor 141. The junction T2a is also connected with thecontact finger 145 while the contact finger 144 is connected with thejunction T2b between the capacitors C1 and C2 and the contact finger 143is connected with the other end T2c of the capacitor C2 which isconnected with the ground.

The contact segments 146 to 148 which are slidably engaged by thecontact fingers 143 to 145 are mounted on a support ring 150 (see FIG.10) which is mounted on one of the tape hubs for integral rotationtherewith. Referring to FIG. 10, there is shown a tape cassette 151which is of the type commonly referred to as a micro-cassette. Thecassette 151 has a pair of tape hubs 152, 153 rotatably disposedtherein, and a length of a magnetic tape Tp has its opposite endssecured on the respective hubs and is disposed thereon. A leader portionof the tape Tp is drawn from the periphery of one hub 152, passed aroundguide rollers, not shown, so as to be disposed in a taut condition alongwindow slots 156, 157, 158, 159 and 160 formed in the front end face151a of the cassette 151. Specifically, the centrally located slot 156is adapted to receive a pinch roller, and the immediately adjacent slots157 and 158 are adapted to receive a record/playback head. And theoutermost slots 159, 160 are adapted to receive an erase head.

An aperture 161 for receiving a capstan is formed to extend through thecassette 151 vertically at a position immediately behind the centralslot 156, the capstan being adapted to feed the tape Tp at a ratedspeed. A pair of cassette positioning apertures 163, 164 are also formedto extend through the cassette vertically at positions immediatelybehind the slots 159, 160. As shown, the tape hubs 152, 153 are formedwith a plurality of inwardly extending projections 152a, 153a which areadapted for engagement between outwardly extending projections from atape supply shaft and a tape take-up shaft provided on the part of thetape recorder when the cassette 151 loaded thereon.

Specifically, the tape recorder is provided with a tape supply shaft 165and a tape take-up shaft 166 which are adapted to fit in the tape hubs152 and 153, respectively. The tape supply shaft 165 comprises a driveshaft 165a which is rotatably mounted, a drive wheel 165b which isintegrally secured to the lower portion of the shaft 165a, a drivesleeve 165c rotatably fitted on the shaft 165a, and a tensiontransmission spring 165d disposed on the shaft 165a intermediate thesleeve and the drive wheel 165b. A rotating drive is imparted from adrive mechanism, not shown, to the drive wheel 165b for rotating thedrive sleeve 165c through the spring 165d. The drive sleeve 165c isprovided with outwardly extending projections 165e which engage betweenthe projections 152a. The tape take-up shaft 166 is constructed in thesimilar manner. Specifically, it comprises a drive shaft 166a which isrotatably mounted, a drive wheel 166b integrally secured to the lowerportion of the shaft 166a, a drive sleeve 166c which is fitted over thetop portion of the shaft 166a and capable of relative rotation thereto,a plurality of outwardly extending projections 166c formed on theperiphery of the sleeve 166c and adapted for engagement between theprojections 153a on the hub 153, and a tension transmission spring 166ddisposed on the shaft 166a at a position above the drive wheel 166b.

The support ring 150 mentioned above is formed of an electricallyinsulating material, and is integrally secured to the lower portion ofthe drive sleeve 166c of the tape take-up shaft 166. The transmissionspring 166d is thus interposed between the support ring 150 and thedrive wheel 166b, and a drive which is externally applied to the drivewheel 166b acts through the spring 166d and the support ring 150 torotate the drive sleeve 166c. The tension springs 165d, 166d form a slipmechanism permitting a slip of the drive sleeve 166c, for example,preventing an increase in the tape speed as the tape continues to betaken up to thereby increase the diameter of the roll on the tapetake-up hub. When the tape reaches its terminal end and the drive sleeve166c ceases to rotate even though a drive continues to be applied to thedrive wheel 166b, the spring 166d permits the drive wheel 166b to slip,preventing the transmission of the drive to the drive sleeve 166 c. Inthis manner, the springs 165d, 166d form friction gearings.

The contact segments 146 to 148 are embedded in the outer periphery ofthe support ring 150 at an equal spacing for engagement by the tips ofthe conductive contact fingers 143 to 145. Each of the fingers 143 to145 comprises a resilient conductive wire material, and has a base endsecured to an electrically insulating holder 168 through which it isconnected with the junctions T2a, T2b and T2c (see FIG. 9),respectively. Each of the contact segments 146 to 148 may comprise ametal foil, for example, having a circumferential length which issufficient to permit a pair of adjacent contact fingers to engage withone of the contact segments simultaneously, but which is insufficient topermit a simultaneous engagement of all of the three contact fingers 143to 145 therewith. When the support ring 150 rotates counter-clockwise,the contact segment 147 is initially engaged by the contact finger 145,for example, and then by contact finger 144. At this time, the segment147 is simultaneously engaged by the contact fingers 145 and 144, andwhen it is engaged by the contact finger 143, the contact finger 145 isdisengaged therefrom, leaving the contact segment 147 engaged by thecontact fingers 144 and 143 simultaneously. The same applies to theremaining contact segments 146 and 148.

Returning to FIG. 9, an audio frequency oscillator 170 is connected withthe amplifier 101 and the tape end detector circuit 140. The oscillator170 is formed by a multivibrator oscillator circuit which is similar tothe oscillator shown in FIG. 1. Thus, it comprises a pair of transistors171, 172 which are cross-linked by resistors 173, 174, 175, 176 andcapacitors 177, 178. An output of the oscillator 170 which is producedat the collector of the transistor 172 is coupled through a couplingcapacitor 180 with the base of the transistor 107 in the amplifier 101.When the oscillator 170 is operative, an output therefrom is fed to theinput of the amplifier 101 through the capacitor 180. The resistors 173to 176 have their one end connected with the collector of the secondswitching transistor 142 in the tape end detector circuit 140, and arefed from a positive bus 108a when the transistor 142 is conductive.

In operation, when a sufficient length of magnetic tape is remaining onthe tape hub 152 which fits over the tape supply shaft 165, the tape isfed at a uniform rate by the cooperation of the capstan and the pinchroller, and is taken up around the periphery of the tape hub 153 whichis rotatively driven by the tape take-up shaft 166. When the tape isrunning, the tape take-up shaft 166 rotates in the counter-clockwisedirection, for example, and such rotation is imparted to the drivesleeve 166c and the support ring 150, which therefore also rotate in thecounter-clockwise direction, thus causing the contact segments 146, 147,148 to be engaged by the three resilient slidable contact fingers 145,144, 143 in a sequential manner. As the contact between the contactsegments and the contact fingers occurs, the capacitors C1 and C2 arealternately short-circuited, preventing them from being charged to agiven value. Specifically, when the rotation of the support ring 150 hascaused the contact segment 147 to be engaged by the contact fingers 144and 145, the capacitor C1 is short-circuited, whereby the charge thereonis discharged. At this time, the charging of the capacitor C2 takesplace through the contact segment 147, but the charge on the capacitorC2 is discharged when the contact segment 147 is engaged by the contactfingers 144 and 143. During the time the charging and discharge takeplace in an alternate fashion or during the time the tape continues torun, the capactors C1, C2 cannot be charged to a given value, so that anoperating voltage of a given value cannot be applied to the base of thefirst switching transistor 141, which therefore remains non-conductive.When the running tape reaches its terminal end under this condition, theabsence of any length of the tape being fed causes the tape hubs 152,153 to cease their rotation. Thereupon, the slip mechanism formed by thesprings 165d, 166d becomes operative to interrupt the rotation of thedrive sleeves 165c, 166c and the support ring 150. Since the contactsegments 146 to 148 also come to a stop, either capacitor C1 or C2 orboth of these capacitors are free to charge up to a given value.

The choice of the particular capacitor or the capacitors which arecharged depends on the angular positions assumed by the contact segments146 to 148 as they come to a stop. Whatever position they may assume asthey come to a stop, it is not possible for both capacitors C1, C2 to beshort-circuited simultaneously, thus allowing at least one of them to becharged. As the selected capacitor is charged, the voltage thereacrossincreases to a value which is sufficient to render the transistor 141conductive. This in turn renders the second switching transistor 142conductive. As a consequence, the transistor 139 is supplied through theresistor 136 with a bias voltage, which causes this transistor toconduct. Thereupon, the loudspeaker 102 is connected across thetransformer secondary coil 121a.

On the other hand, when the second transistor 142 conducts, theoscillator 170 is fed from the bus 108a through the conductingtransistor 142, whereby an output signal of an audio frequency iscoupled therefrom through the capacitor 180 to the base of thetransistor 115 contained in the amplifier 101 of the tape recorder. Thesignal is amplified by the amplifier 101 and appears across thetransformer secondary coil 121a of the output transformer 121,permitting the loudspeaker 102 which is connected thereacross throughthe conducting transistor 139 to give off an audible alarm indicative ofthe fact that the running tape Tp has reached its terminal end. While inthe embodiment described, the contact segments have been mounted on thetape take-up shaft 66, they may be mounted on the tape supply shaft 65.

In the case when a cassette tape recorder in which the tape end warningapparatus including the tape end detector circuit 140 is incorporatedhas a pause mechanism, as inconvenience is caused in that the tape endwarning apparatus operated in response to the depression of a pausebutton such an interruption of the tape running results in theinterruption of the rotation of the tape hubs 152, 153 (see FIG. 10)concurrently. As is well recognized, the pause mechanism operates byinterrupting the energization of a tape drive motor by a pause switch.In other words, the amplifier and other electrical circuits aremaintained energized while the energization of only the tape drive motoris interrupted to bring the tape to a stop. This results in stopping thetape take-up and supply shafts and hence the tape hubs which theyengage.

FIG. 11 shows another arrangement of the tape end warning apparatuswhich avoids the above mentioned inconvenience, by feeding the tape endwarning apparatus through a switch which is operated in response to apause button. Referring to FIG. 11, the circuit arrangement shown isgenerally similar to that shown in FIG. 9 except that a switch SW1 isconnected in the positive bus 108a, the switch being adapted to beoperated in response to a pause button, not shown. A tape drive motor Mand a motor speed control circuit 190 are connected so as to be fedthrough the switch SW1. The switch SW1 normally remains closed, so thatthe motor M and the circuit 190 are energized to permit a tape runningand to permit the tape end detector circuit 140 and the oscillator 170to operate when a terminal end of the running tape is reached, thusallowing the tape end to be warned. However, when the pause button isoperated to open the switch SW1, the motor M and the circuit 190 aredeenergized, and simultaneously the tape end detector circuit 140 andthe oscillator 170 are also deenergized, preventing their operation. Inthis manner, an audible alarm cannot be produced when the pause buttonis operated, thus eliminating the above inconvenience.

In the embodiment shown, it should be noted that the oscillator 170 maybe omitted and instead the collector-base path of the transistor 139utilized to provide a positive feedback across the amplifier 101 so asto cause an oscillation thereof, thus allowing the loudspeaker 102 togive off an audible alarm. Such an arrangement is shown in FIG. 12.Referring to FIG. 12, an amplifier 201 of a tape recorder is shown in ablock 201A shown by phantom lines. The amplifier 201 is operative,during a playback mode of the tape recorder, to amplify an output signalreproduced by a playback head, not shown, and to supply it to aloudspeaker 202, and is also operative, during a record mode of the taperecorder, to amplify an output signal from a microphone, not shown, andto supply it to a record head, not shown. The amplifier 201 isconventional and is generally similar to the circuit arrangement of theamplifier 101 shown in FIG. 9 except for a minor change which will bedescribed later. Therefore, parts or circuit elements shown in FIG. 12which correspond to those of FIG. 9 are represented by like referencecharacters added with 100, and the details of the circuit connectionwill not be described herein. However, the circuit arrangement shown inFIG. 12 differs from that of FIG. 9 in that the base of a transistor239, which corresponds to the transistor 139, is connected to thejunction between the collector of transistor 207 and capacitor 214(corresponding to elements 107 and 114 shown in FIG. 9) through a seriescombination of a switch 238 and a resistor 228. The collector of thetransistor 239 is connected with the stationary contact 233b of theearphone jack 233 while the emitter is connected with the otherstationary contact 234c of the changeover switch 234. The base of thetransistor 239 is supplied with an operating voltage for conduction,through the switch 238 as it is closed. The resistor 228 has aresistance which assures a proper operating voltage to the base of thetransistor 239, its value being dependent on the resistance of theresistor 210. The resistor 228 may be omitted when the resistor 210 hassufficient value.

The alarm switch 238 is a normally open switch constructed in a mannersimilar to the switch 38 shown in FIG. 2. Thus, it is disposed in thepath of rocking motion of movable member 49 which supports supply shaft48 for the tape Tp, and is adapted to be closed by the member 49 as aresult of an increase in the tape tension as the terminal end of thetape Tp is reached.

In operation, in either the record or playback mode of the taperecorder, the alarm switch 238 is closed when the terminal end of therunning tape is reached. When the switch is closed, a forward bias isapplied through the resistors 210, 228 and the closed switch 238 to thebase of the transistor 239 to render it conductive, whereupon theloudspeaker 202 is connected across the secondary coil 221a and apositive feedback is also applied across the output and the input of theamplifier 201 through a path including the collector-base path of thetransistor 239, switch 238 and resistor 228 to drive the amplifier 201into oscillation. The oscillation output is converted into an audiblealarm by the loudspeaker 202, indicating that the terminal end of therunning tape Tp has been reached.

FIG. 13 shows a modification of the circuit arrangement shown in FIG. 12in which a changeover switch 240 is provided so as to be operated inganged relationship with the record/playback changeover switch 234 sothat an audible alarm indicative of the tape end in only given offduring a record mode of the tape recorder. Specifically, the earphonejack 233 has its stationary contact 233b connected with one end of thesecondary coil 221a of the output transformer 221 contained in theamplifier 201 (see FIG. 12) of the tape recorder. The other end of thesecondary coil 201a is connected with the negative bus 209. The movablecontact 233a of the jack 233 is connected with the movable contact 234aof the record/playback changeover switch 234 and is thrown to thestationary contact 234b, during a record mode and thrown to thestationary contact 234c during a playback mode of the tape recorder. Themovable contact 233a is normally maintained in contact with thestationary contact 233b. The loudspeaker 202 is connected between thestationary contact 234c of the switch 234 and the bus 209. Instead ofbeing connected with the negative bus 209, the other stationary contact233c of the jack is connected with the movable contact 240a of achangeover switch 240 having a pair of stationary contacts 240b and240c, one of the stationary contacts, 240b, being connected through theresistor 235 to the bus 209 and the other stationary contact 240c beingdirectly connected to the bus 209. The stationary contact 234b of theswitch 234 is connected with the stationary contact 240b of the switch240. The transistor 239 has its base connected with one terminal of theswitch 238, its collector connected with the stationary contact 233c andits emitter connected with the stationary contact 234c of the changeoverswitch 234.

In operation, during a record mode of the tape recorder, therecord/playback changeover switch 234 assumes a position in which itsmovable contact is thrown to the stationary contact 234b, and at thesame time, the changeover switch 240 assumes a position in which itsmovable contact is thrown to the stationary contact 240b. When therunning tape Tp reaches its terminal end under this condition, anincrease in the tape tension causes the switch 238 to be closed in asimilar manner similar to that mentioned above. Then a forward bias isapplied from the positive bus 208 through the resistors 210, 228 and theclosed switch 238 to the base of the transistor 239 to render itconductive. When transistor 239 conducts, the loudspeaker 202 isconnected across the secondary coil 201a, and in addition, a positivefeedback is established from the secondary coil to the input of theamplifier 201 through a path including the collector-base path of thetransistor 239, switch 238 and resistor 228. This causes the amplifier201 to oscillate, whereby an oscillation output is given off by theloudspeaker 202 as an audible alarm.

In a playback mode of the tape recorder, the record/playback changeoverswitch 234 has its movable contact thrown to the stationary contact234c, thus connecting the loudspeaker 202 across the secondary coil201a. The switch 240, which is ganged with the switch 234, has itsmovable contact thrown to the stationary contact 240c, thus connectingthe stationary contact 233c of the jack 233 with the bus 209. Thus, theclosure of the switch 238, which occurs as the tape Tp reaches itsterminal end, does not render the transistor 239 conductive, but merelyremoves the reproduction of sound by the loudspeaker 202, whichindicates the end of the tape running.

FIG. 14 shows a further circuit arrangement in which a changeover switchganged with the record/playback changeover switch is provided betweenthe switching transistor 239, and an oscillator which produces arecording bias, thereby enabling the activation of an audible alarm onlyduring a record mode of the tape recorder. Referring to FIG. 14, it willbe noted that the circuit arrangement inclusive of an amplifier 301 ofthe tape recorder as well as the earphone jack 233, changeover switch234, loudspeaker 202 and switching transistor 239 remains the same asthat shown in FIG. 12, and therefore will not be repeatedly described.The only difference over the arrangement of FIG. 12 is found in thesubstitution of a capacitor 328 for the resistor 228 shown in FIG. 12.

In FIG. 14, the junction between the capacitor 328 and the alarm switch238 is connected with one end of a resistor 340, the other end of whichis connected with a stationary contact 341b of a changeover switch 341which is ganged with the record/playback changeover switch 234. Theswitch 341 has a movable contact 341a which is connected with a sourceof positive voltage and which is thrown to the contact 341b during arecord mode of the tape recorder in order to feed power to a biasoscillator 342.

The bias oscillator 342 is of a conventional design, and comprises anoscillation transformer 343, oscillation transistor 344, resistors 345,346, 347 and capacitors 357, 358. When the changeover switch 341 is in aposition to feed the bias oscillator 342, the latter supplies a biasvoltage to a record head, not shown, as indicated by an arrow T3b.During a playback mode of the tape recorder, the movable contact 341a isthrown to another stationary contact 341c which is an idle contact,whereby the oscillator 342 is rendered inoperative.

In operation, during a record mode of the tape recorder, the movablecontact 341a of the switch 341 is thrown to its stationary contact 341b,whereby power is supplied to the oscillator 342 for applying a biasvoltage to the record head, not shown. When the running tape Tp reachesits terminal end, the resulting increase in the tape tension causes theswitch 238 to be closed. When the switch 238 is closed, a forward biasis applied through the resistor 340 and the closed switch 238 to thebase of the transistor 239 to render it conductive. Thereupon, theloudspeaker 202 is connected across the transformer secondary coil 221a,and simultaneously, a positive feed back is applied across the amplifier301 through a path including the collector-base path of the transistor239, switch 238 and capacitor 328. Thus the amplifier 301 is driven intooscillation, and an oscillation output is given off by the loudspeaker202 as an audible alarm.

During a playback mode of the tape recorder, the movable contact 341a ofthe switch 341 is thrown to its other stationary contact 341c, so thatthe bias oscillator 342 remains inoperative. However, the movablecontact 234a of the record/playback changeover switch 234 is thrown tothe stationary contact 234c, connecting the loudspeaker 202 across thetransformer secondary coil 221a. When the terminal end of the runningtape is reached, the loudspeaker ceases to reproduce any sound, whichsignifies to the operator of the end of the tape running. The closure ofthe alarm switch 238 remains without effect because the movable contact341a is thrown to the stationary contact 341c, and the resultingnon-conduction of the transistor 239 prevents the positive feedbackacross the amplifier 301 from becoming effective.

It will be noted that the arrangement shown in FIG. 13 which utilizesthe changeover switch 240 ganged with the record/playback changeoverswitch 234 to connect the collector of the transistor 239 with theground or the negative bus 209 in order to prevent the switchingtransistor 239 from being rendered conductive during a playback mode, orthe arrangement shown in FIG. 14 which utilizes the changeover switch341 associated with the bias oscillator 342 to render the switchingtransistor 239 inoperative during a playback mode can equally be appliedto the switching transistor 39 in the tape end warning apparatus 1Bshown in FIG. 1.

Conversely, the arrangement shown in FIG. 5 which connects the collectorof the switching transistor 39 with the movable contact 33a of theearphone jack 33 so that the series combination of the transistor 39 andthe loudspeaker 2 may be disconnected from the output transformer 21when an earphone plug is inserted into the jack to thereby prevent anaudible alarm from being produced by the loudspeaker 2 can also beapplied to the arrangement shown in FIG. 12 where a positive feedbackacross the amplifier 201 is utilized to drive it into oscillation.However, it should be noted that when so applied, the non-conduction ofthe switching transistor 239 results in the interruption of the positivefeedback path and hence the failure of the amplifier 201 to oscillate,thus preventing either loudspeaker 202 or earphone from giving off anaudible alarm during a secret recording.

Additionally, the arrangement shown in FIGS. 9 to 11 which utilize thepair of capacitors C1 and C2 which are short-circuited by the selectiveengagement of the contact fingers 143 to 145 with the contact segments146 to 148 during a tape running but which are allowed to be charged upto produce a tape end detection signal upon interruption of the taperunning may also be applied to the self-oscillation circuit shown inFIG. 12 in addition to the circuit arrangement of FIG. 1. A combinedcircuit arrangement is specifically illustrated in FIG. 15, whichhowever will not be specifically described since the individual circuitshave been fully described above.

Furthermore, the use of the diode 56 shown in FIG. 4, the delay circuit60 shown in FIG. 6 or the means for preventing a howling effect asillustrated in FIGS. 7 and 8 is not limited to the warning apparatusshown in FIG. 1, but may equally be applied to the warning apparatusshown in FIG. 12.

The means illustrated in FIG. 6 for preventing an alarm due to contactclosures which may be caused by vibrations of the tape recorder and themeans of FIG. 7 which prevents a howling effect may be used incombination, as shown by a circuit diagram of FIG. 16. In this instance,the resistor 64, capacitor 65 and the emitter of the transistor 62 inthe delay circuit 60 are connected in common with the emitters of bothtransistors 40, 41 in the oscillator 36, and connected with the movablecontact 38a of the alarm switch 38, the stationary contact 38b of whichis connected with the ground. This permits a convenient part of thecasing of the tape recorder to be utilized as the stationary contact 38bfor cooperation with an insulated movable contact, thus allowing theswitch construction to be simplified. A resistor 359 is shown connectedbetween the base of the transistor 69 and the junction between the anodeof the diode 56 and the collector of the transistor 61 to assure asufficient voltage level is supplied to the oscillator 36.

What is claimed is:
 1. A tape end warning apparatus for use in a taperecorder of the type which includes an audio amplifier, a loud speaker,a first switch for connecting an output of said amplifier to saidloudspeaker when said tape recorder is in a playback mode and fordisconnecting said output of said amplifier to said loudspeaker whensaid tape recorder is in a record mode, a tape cassette receivingchamber, a drive shaft extending into said receiving chamber and adaptedto engage a drive shaft recess in a tape cassette when a tape cassetteis placed within said receiving chamber, and drive means for drivingsaid drive shaft, said tape end warning apparatus comprising:a feedbackcircuit, including a normally open switch, forming an electricalfeedback path between said output and an input of said amplifier whensaid normally open switch is closed; an end tape detecting means forclosing said normally open switch when an end of tape condition isdetected, said end of tape detecting means including: (1) a lever whichis pivotable about a predetermined axis, said lever rotatably supportingsaid drive shaft at a point spaced from said axis, said lever adapted topivot when the tension of a tape carried by a cassette placed in saidreceiving chamber increases due to an end of tape condition; and (2)said lever adapted to close said normally open switch when said lever isrotated due to said end of tape condition whereby said feedback circuitconnects the output of said amplifier to the input of said amplifier andsaid loudspeaker generates an audible alarm signal.
 2. The tape endwarning apparatus of claim 1, further including means for disabling saidfeedback circuit when said recorder is operating in said playback modewhereby said audible alarm signal is not generated when said taperecorder is in said playback mode.
 3. The tape end warning apparatus ofclaim 2, wherein said amplifier includes an output transformer, saidfeedback circuit includes a transistor which is rendered conductiveduring a record mode when said normally open switch is closed, saidtransistor forming part of said electrical feedback path between saidoutput and said input of said amplifier and wherein said disabling meanselectrically connects said output transformer to said transistor whensaid tape recorder is in said record mode and electrically disconnectssaid output transformer from said transistor when said tape recorder isin said playback mode.
 4. A tape end warning apparatus for use in a taperecorder of the type which includes an audio amplifier and a firstswitch for connecting an output of said amplifier to said loudspeakerwhen said tape recorder is in a playback mode and for disconnecting saidoutput of said amplifier to said loudspeaker when said tape recorder isin a record mode, said tape end warning apparatus comprising:a feedbackcircuit, including a normally open switch, forming an electricalfeedback path between said output and an input of said amplifier whensaid normally open switch is closed; and an end of tape detecting meansfor closing said normally open switch when an end of tape condition isdetected.
 5. The tape end warning apparatus of claim 4, furtherincluding means for disabling said feedback circuit when said taperecorder is operating in said playback mode.
 6. The tape end warningapparatus of claim 5, wherein said amplifier includes an outputtransformer, said feedback circuit includes a transistor which isrendered conductive during a record mode when said normally open switchis closed, said transistor forming part of said electrical feedback pathbetween said output and said input of said amplifier and wherein saiddisabling means electrically connects said output transformer to saidtransistor when said tape recorder is in said record mode andelectrically disconnects said output transformer from said transistorwhen said tape recorder is in said playback mode.
 7. The tape endwarning apparatus of claim 1 or 4, further including:a record biasoscillator for generating a bias voltage which is applied to a magnetichead included in said tape recorder whenever a power supply is appliedthereto; and switch means coupled to said first switch for applying saidpower supply to said record bias oscillator whenever said recorder is insaid record mode and for disconnecting said power supply from saidoscillator whenever said recorder is in said playback mode.
 8. A tapeend warning apparatus for use in a tape recorder, comprising an alarmswitch adapted to be closed when a running tape reaches its terminalend, and a switching transistor adapted to be forward biased intoconduction upon closure of the switch for connecting a loudspeakeracross the output of an amplifier contained in the tape recorder and forforming a electrical feedback path across the output and input of theamplifier to drive it into oscillation, thereby enabling an oscillationoutput to be given off by the loudspeaker as an audible alarm when therunning tape reaches its terminal end.